Method, system and module for monitoring a power generating system

ABSTRACT

A sensing module positioned about an optical fiber cable having a long axis. The optical fiber includes a core that transmits light through the optical fiber cable. The sensing module includes a first short-period fiber grating positioned about the core. A second short-period fiber grating is positioned about the core and at a distance along the long axis with respect to the first short-period fiber grating. At least one of a long-aperiod fiber grating and a long-period fiber grating is positioned between the first short-period fiber grating and the second short-period fiber grating. A fiber cladding is positioned around the long-period grating and/or the long-aperiod grating of the sensing module. A sensing skin is positioned about the fiber cladding and includes a chemical gas active material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Division of U.S. patent application Ser. No.11/284,595 entitled “Method, System and Module for Monitoring a PowerGenerating System” filed Nov. 22, 2005, now U.S. Pat. No. 7,151,872which is herein incorporated by reference

BACKGROUND OF THE INVENTION

This invention relates generally to power generating systems and, moreparticularly, to a method and system for emission control and combustionoptimization in fossil fuel fired boilers with an array of fibergrating-based sensing modules.

In numerous industrial environments, a hydrocarbon fuel is burned instationary combustors (e.g., boilers or furnaces) to produce heat toraise the temperature of a fluid, e.g., water. For example, the water isheated to generate steam, and this steam is then used to drive turbinegenerators that output electrical power. Such industrial combustorstypically employ an array of many individual burner elements to combustthe fuel. In addition, various means of combustion control, such asoverfire air, staging air, reburning systems and selective non-catalyticreduction systems, can be employed to enhance combustion conditions andreduce emissions of oxides of nitrogen (NO_(x)) and carbon monoxide.

Emissions and efficiency are key performance metrics for industrialboilers that are often used for generation of process steam required forindustries. Emissions and efficiency are important performance metricsfor utility boilers, which are mainly used for power generation alongwith generation of process steam. Poor or non-uniform combustion leadsto low availability, low peak steam/power generation, low efficiency andhigh emissions. Conventional industrial boiler and utility boilercontrols are often based on data driven or empirical models with limitedfeedback from the boiler environment due to limited real-time,multi-point monitoring and sensing capabilities. Most sensing systemsthat are used to monitor NO_(x), CO and temperature use single-pointsensors that are typically placed in the boilers exhaust area. Often,gas sensing is ex-situ and extractive in nature.

For a combustion system, such as a multiple burner boiler furnace or agas turbine combustor, to operate efficiently and to produce anacceptably complete combustion that generates byproducts falling withinthe limits imposed by environmental regulations and design constraints,all individual burners in the combustion system must operate cleanly andefficiently and all combustion modification systems must be properlybalanced and adjusted. Emissions of NO_(x), carbon monoxide (CO),mercury (Hg) and/or other byproducts generally are monitored to ensurecompliance with environmental regulations and acceptable systemoperation. Such operating conditions and/or gas emissions can bemonitored using sensors.

Due to non-uniform combustion, power generation oriented utility boilersor process steam generating industrial boilers tend to operate at lowerefficiencies than the design limits, thus resulting in high operatingand maintenance costs. In addition, limited sensing and actuationcapabilities and limited real-time information regarding boilercondition leads to solutions that are not very effective for reducingemissions or improving efficiency. Many conventional industrial orutility boilers suffer in this context and provide only limitedimprovements in emission reduction and/or efficiency.

Conventional electric-based gas sensors operate at temperatures lessthan about 500° C. due to sensing material and/or device limitations.The reliability of conventional electric-based gas sensors has sufferedfrom several problems. These gas sensors fail to operate when theenvironmental temperature is higher than the sensor's operatingtemperature. It is also difficult to predict the gas concentration dueto the temperature-dependent nonlinear sensitivity characteristics.Additionally, electric-based gas sensors suffer from long-term stabilityor sensitivity degradation due to thermal effects on the electricalinterfaces to supply power or transmitting signal. Further, they are notsuitable for high-voltage and explosive environments. Finally,electric-based sensors are not suitable for multiple point gas sensingapplications.

Solid-state semiconductor gas sensing technology generally performsbetter than the electrochemical gas sensing technology due to the use ofa wide band-gap material that allows high temperature operation up to500° C. Despite the drift due to the temperature-dependent resistivityat higher temperature, solid-state semiconductor gas sensors provide anacceptable performance as a point sensor. However, these devices alsotend to fail at higher temperatures due to thermal effects on theelectrical interfaces to supply power or a transmitting signal as well.Further, because the sensing performance varies significantly withenvironmental temperature, pressure variations and/or toxic gasvariations, solid-state semiconductor gas sensors require a constantcalibration to maintain accuracy.

There is no systematic method to adjust the air and fuel flows forreducing spatial variance of emissions at a boiler's exit to reducestack emissions. Rather, conventional boiler combustion optimizationprocedures are primarily established using the boiler expert's domainknowledge. Data-driven models such as Neural Networks and Expert Systemslack the rigor and fidelity and thereby have limited impact onefficiency because these models are dependent on data quality and areprone to data noise and inaccuracies. Model-based optimization systemsthat incorporate the physics of the combustion system along withaccurate and spatially dense data provided by a fiberoptic sensor arrayovercome the limitations of currently available boiler optimizationproducts that rely on data limited in terms of availability, accuracyand spatial density due to the harsh environment of boiler systems andsensor capability limitations.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides a sensing modulepositioned about an optical fiber cable having a long axis. The opticalfiber cable includes a core that transmits light through the opticalfiber. The sensing module includes a first short-period fiber gratingpositioned about the core. A second short-period fiber grating ispositioned about the core and at a distance along the long axis withrespect to the first short-period fiber grating. At least one of along-aperiod fiber grating and a long-period fiber grating is positionedbetween the first short-period fiber grating and the second short-periodfiber grating. A fiber cladding is positioned about the long-aperiodfiber grating and/or the long-period fiber grating. A sensing skinhaving a chemical gas active material is positioned about the fibercladding.

In another aspect, a system for monitoring operating conditions of apower generating system is provided. The system includes an opticalfiber sensing cable that extends through at least a portion of the powergenerating system. The optical fiber sensing cable has a core. An arrayof sensing modules is positioned along the optical fiber sensing cable.Each sensing module includes a plurality of fiber gratings formonitoring at least one power generating system operating condition. Abroadband light source emits a light through the fiber core. An opticalcoupler in communication with the light source transmits a portion ofthe light through the fiber core and a fiber grating structure reflectsa portion of the light from the plurality of fiber gratings to aphotodetector.

In another aspect, the present invention provides a method formonitoring operating conditions of a power generating system. The methodincludes providing a sensing system including an optical fiber sensingcable that extends at least partially with respect to the powergenerating system. The optical fiber sensing cable has a fiber core thatextends along a long axis of the optical fiber sensing cable. An arrayof multi-functional sensing modules each is positioned about the fibercore at a spatial location of the power generating system. A modifiedfiber cladding including a sensing material with chemical gassensitivity surrounds each multi-functional sensing module. A broadbandlight is propagated through the fiber core. At least one operatingcondition is detected at least one spatial location. A light signal isreflected by at least one multi-functional sensing module or transmittedto a near infrared photodetector. Within the photodetector, the lightsignal is processed and a corresponding electrical signal iscommunicated to a computer interfaced with the sensing system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic view of a power generating system that includes afossil fuel fired boiler;

FIG. 2 is a schematic view of the fossil fuel fired boiler shown in FIG.1;

FIG. 3 is a schematic view of a sensing system for monitoring theoperating conditions and/or parameters of the power generating system;

FIG. 4 is a perspective view of a sensing module for the sensing systemschematically shown in FIG. 3;

FIG. 5 is a schematic view of a sensing module for the sensing systemschematically shown in FIG. 3;

FIG. 6 is a graphical representation of transmission versus wavelengthfor a signal transmitted through the sensing module shown in FIG. 5;

FIG. 7 is a graphical representation of power loss versus wavelength fora signal transmitted through the sensing grating element shown in FIG.5;

FIG. 8 is a schematic view of an evanescent wave field profile and itscoupling back to fundamental mode in the gas sensing grating through thesensing module shown in FIG. 5;

FIG. 9 is a graphical representation of power loss versus wavelength fora signal reflected by the sensing module shown in FIG. 8; and

FIG. 10 is a graphical representation of power loss versus wavelengthfor a signal transmitted through the sensing grating between the fiberBragg gratings shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a sensing method and system formonitoring operating conditions and/parameters of a power generatingsystem, such as, without limitation, a fossil fuel fired boiler, a gasturbine and a steam turbine. As an exemplary embodiment, the inventionwill be described in the context of a boiler system. The sensing methodand system detect the presence of gases and/or the concentration of thegases produced a combustion process within the boiler furnace, as wellas other operating conditions and/or parameters including, withoutlimitation, temperature, heat flux and/or pressure. The sensing methodand system includes an array of sensing modules each positioned at aspatial location within the power generating system to monitor operatingconditions and/or parameters, such as combustion conditions that includeemissions, temperature and/or pressure. The sensing method and systemalso includes using the detected information to make adjustments toboiler system parameters, such as burner air to fuel ratio, totalairflow and fuel flow to the boiler, to yield optimized boilerperformance objectives as indicated by the in-furnace sensors. Optimizedperformance includes, for example CO and NO_(x) emissions, reducedbyproducts emissions, increased efficiency, increased power output,improved superheat temperature profile and/or reduced opacity. Boilersystem adjustments include, for example, adjusting or tuning mill (a setof burners) level coal and air flow, individual burner fuel to airratio, overfire airflows and other furnace input settings such as totalairflow and total fuel flow to the boiler plant.

By implementing multi-point, in-situ gas sensors that operate closer tocombustion areas, i.e. upstream of exhaust, the effectiveness ofmodel-based combustion optimization methods can be greatly improved,thus improving boiler efficiency and reducing emissions. Principally,the accuracy of empirical models such as Computational Fluid Dynamicsbased models or data driven models such as Neural Networks used by suchoptimization methods is greatly improved by the improved accuracy andspatially more dense information provided by the fiber optic basedmulti-point, multi-parameter sensing system.

A schematic view of a power generating system 10 is shown in FIG. 1. Inone embodiment, power generating system 10 includes a boiler 12 coupledto a steam turbine-generator 14. Steam is produced in boiler 12 andflows through steam pipe 16 to generator 14. Boiler 12 burns a fossilfuel, such as coal, in a boiler furnace 18 which produces heat toconvert water into steam used to drive generator 14. In alternativeembodiments, the fossil fuel burned in boiler 12 can include oil ornatural gas. Crushed coal is stored in a silo 20 and is further groundor pulverized into fine particulates by a pulverizer or mill 22. A coalfeeder (not shown) adjusts the flow of coal from coal silo 20 into mill22. An air source, for example, fan 26 is used to convey the coalparticles to furnace 18 where the coal is burned by burners 28. The airused to convey the coal particles from mill 22 to burners 28 is referredto as primary air. A second fan 30 supplies secondary air to burners 28through air conduit and a windbox 32. The secondary air is heated bypassing through a regenerative heat exchanger 34 located in a boilerexhaust line 36. The combustion gas exits boiler 18 at an exit 37.

In one embodiment, the combustion gas is directed through boiler exhaustline 36 through a selective catalyst reduction device (“SCR”) 38 toreduce NO_(x) contained in the combustion gas. Within SCR 38, NO_(x) isreduced to nitrogen and oxygen. An electrostatic precipitator (“ESP”) 40is positioned downstream of SCR 38. The combustion gas enters ESP 40.Within ESP 40, a portion of a particulate matter contained within thecombustion gas is removed or precipitated out of the combustion gas asthe combustion gas is directed through ESP 40. A fan 42 directs thefiltered combustion gas through a suitable exhaust pipe or chimney 44 toexhaust gases generated during the combustion process from powergenerating system 10.

Referring also to FIG. 2, boiler furnace 18 includes an array 50 ofmulti-functional sensing modules 52, 53, 54, 55 and/or 56 located withrespect to at least a portion of power generating system 10. In oneembodiment, array 50 is positioned with respect power generating system10 and, more particularly, with respect to boiler 12. For example, atleast one multi-functional sensing module 52, 53, 54, 55 and/or 56, asdiscussed in greater detail below, is positioned at a spatial locationwithin boiler furnace 18, with respect to exit 37 of boiler furnace 18,with respect to generator 14 and/or within exhaust chimney 44.Multi-functional sensing modules 52, 53, 54, 55 and/or 56 monitor thecombustion process occurring within boiler furnace 18 as well as theconstituents of the combustion gas generated during the combustionprocess and exhausted from power generating system 10. Array 50 providesdirectly correlated and indirectly correlated (relative) measurements.Combustion quality indications can be obtained from absolutemeasurement, relative measurement and drawing from analysis offluctuations in combustion quality indicator sensor signals. Eachmulti-functional sensing module 52, 53, 54, 55 and 56 monitors thecombustion process conditions and/or parameters at a spatial locationincluding, without limitation, optical radiation, temperature,vibrations, carbon monoxide (CO) emission, carbon dioxide (CO₂)emission, NO_(x) emission, total hydrocarbons (THC) emission, volatileorganic compounds (VOC) emission, sulfur dioxide (SO₂) emission, heatflux, radiance, opacity, emissivity, moisture, hydroxyl radicals (OH)emission, sulfur trioxide (SO₃) emission and/or particulate matteremission.

Referring further to FIGS. 3-6, in one embodiment, a sensing system 60includes array 50 to monitor the operating conditions and/or parametersof power generation system 10 and, more particularly, the operatingconditions and/or parameters of boiler 12. Such operating conditionsand/or parameters include, but are not limited to, internaltemperatures, pressures, seismic variations and/or the presence andconcentration levels of chemical combustion gases generated withinboiler 12 and emitted from power generating system 10. A control system61, as shown in FIG. 2, is in operating control communication withsensing system 60 to receive signals generated as a result of sensordetection and to control the operation of boiler 12 to reduce emissionsand increase boiler efficiency by controlling burner fuel to air ratiosand/or total airflow to the boiler system. In one embodiment, efficiencyis optimized by reducing fouling and/or slag, for example by using thesensed temperatures, strains or pressures to detect a level of slagand/or fouling.

In one embodiment, sensing system 60 includes an optical fiber cable 62that is positioned with respect to and extends along the components ofpower generating system 10. For example, optical fiber cable 62 extendsthrough boiler 12 towards exhaust chimney 44. As shown in FIG. 4,optical fiber cable 62 includes a central fiber core 64 formed of adoped silica that extends along a long axis 63 and having a diameter ofabout 5 microns to about 9 microns. In a particular embodiment, fibercable 64 includes a periodic modulated refractive index structure. Afiber cladding 66 circumferentially covers fiber core 64 and has anouter diameter of about 125 microns made from pure silica. In oneembodiment, fiber cladding 66 is configured to act as a waveguide forlight propagation through fiber core 64. Broadband light source 70,shown in FIG. 3, is positioned in light emitting communication withoptical fiber cable 62 and emits a near infrared light that propagatesthrough fiber core 64.

An optical coupler or circulator 72, schematically shown in FIG. 3, isin light communication with light source 70. Optical coupler 72 receivesthe light transmitted from light source 70 and transmits a portion ofthe light through fiber core 64 of optical fiber cable 62 and a fibergrating structure reflects and/or redirects a portion of the lightthrough a second optical fiber 73 to a photodetector 74 positioneddownstream.

In one embodiment, sensing system 60 includes array 50 ofmulti-functional sensing modules 52, 53, 54, 55 and/or 56 positionedalong optical fiber cable 62 extending through power generating system10. Referring to FIGS. 3-5, in a particular embodiment, array 50includes multi-functional sensing module 52 positioned within boilerfurnace 18 to monitor fouling and/or slag by using temperature, strainand/or pressure sensing. Additionally, multi-functional sensing modules53, 54 and/or 55 are positioned within boiler furnace 18 at spatiallocations, such as at exit 37 of boiler 12, to monitor the presenceand/or concentration of constituents of the combustion gas, such as CO,O₂, NO_(x)and/or H₂ for combustion control and optimization. Further,multi-functional sensing module 56 is positioned with respect to exhaustchimney 44 to monitor the presence and/or concentration of constituentsof the combustion gas downstream from boiler 12. Additionalmulti-functional sensing modules, such as multi-functional sensingmodule 57 and/or 58, are positioned with respect to power generatingsystem 10 to monitor the operating conditions and/or parameters forpower generating system 10, as desired.

Although array 50 shown in FIGS. 2 and 3 includes five multi-functionalsensing modules 52, 53, 54, 55 and/or 56, it is apparent to thoseskilled in the art and guided by the teachings herein provided that inalternative embodiments, array 50 includes any suitable number ofmulti-functional sensing modules, either less than five or greater thanfive. In an alternative embodiment, in addition to multi-functionalsensing modules 52, 53, 54, 55 and/or 56, array 50 includesmulti-functional sensing module 57 positioned with respect to generator14 to monitor the presence and/or concentration of CO and/or thetemperature within generator 14, which may exceed 1000° C., and/ormulti-functional sensing module 58 positioned with respect to exhaustchimney 44 to monitor the emission of exhaust gas including, withoutlimitation, CO, CO₂ and/or H₂S in order to adhere to governmental and/orenvironmental safety standards and/or parameters.

As shown in FIG. 3, the light is transmitted or propagated through fibercore 64, with multi-functional sensing module 52, 53, 54, 55 and/or 56positioned about fiber core 64, and into photodetector 74. As the lightis transmitted through multi-functional sensing module 52, 53, 54, 55and/or 56, light having a selected wavelength is reflected by the fibergrating structure. The reflected light wavelength corresponds to atleast one operating condition and/or parameter, such as CO, NO_(x)and/ortemperature, detected by multi-functional sensing module 52, 53, 54, 55and/or 56. Multi-functional sensing module 52, 53, 54, 55 and/or 56reflects and/or redirects the light to generate a light signal thatdepends upon the measurands. The light signal generated bymulti-functional sensing module 52, 53, 54, 55 and/or 56 is transmittedto photodetector 74 wherein the light signal is processed and/ortransmitted to a computer 76 interfaced and/or communicating withsensing system 60. For example, in one embodiment, a wireless interface78 transmits electrical signals to computer 76 generated byphotodetector 74 in response to light signals received frommulti-functional sensing module 52, 53, 54, 55 and/or 56.

Referring to FIGS. 4, 5 and 8, in one embodiment, multi-functionalsensing module 52, 53, 54, 55 and/or 56 has a length along long axis 63of optical fiber cable 62 of about 20 millimeters to about 50millimeters. In this embodiment, multi-functional sensing module 52, 53,54, 55 and/or 56 includes two short-period fiber gratings 80, 82. Atleast one long-aperiod fiber grating (LAG) 84 and/or at least onelong-period fiber grating (LPG) 86 is positioned between short-periodfiber gratings 80, 82, and generally indicated in FIGS. 4, 5 and 8 assensing element reference number 84/86. In one embodiment, LAG 84 and/orLPG 86 have a modulation along long axis 63 with a pitch size of about100 microns to about 600 microns. LAG 84 and/or LPG 86 are configured toeffectively shed a fundamental mode energy to fiber cladding 66 andradiation modes. First short-period fiber grating 80, secondshort-period fiber grating 82, LAG 84 and LPG 86 each has a length alonglong axis 63 of about 5 millimeters to about 30 millimeters. Further, aspacing 88 is defined between adjacent fiber gratings 80, 82, 84 and/or86 of about 10 millimeters to about 50 millimeters.

Multi-functional sensing module 52, 53, 54, 55 and/or 56 includes amodified cladding or sensing skin 90 positioned about fiber cladding 66,as shown in FIG. 4. Sensing skin 90 is configured to effectively assistthe coupling of fiber cladding 66 to the fundamental mode. Sensing skin90 includes a sensing or chemical gas active material including at leastone base material, such as SnO₂, WO_(X), TiO₂, Fe₂O₃ and Ga₂O₃, that isdoped with material nanoparticles, such as Pd, Pt, Au, Ag, Ni and CuOparticles. The material nanoparticles have a diameter of about 5 nm toabout 10 nm. In one embodiments, sensing skin 90 includes a sensingmaterial with chemical gas sensitivity, which is sensitive and/oractivated by interactions with a chemical gas. In a particularembodiment, multi-functional sensing module 52, 53, 54, 55 and/or 56 ofarray 50 is configured to detect the presences of CO, NO_(x), O₂, H₂ andor H₂S. It is apparent to those skilled in the art and guided nu theteachings herein provided that sensing skin 90 can be fabricated using adoping process to sense or detect any desired chemical gas.

In one embodiment, sensing skin 90 includes a sensing material that issensitive to the presence of CO. For example, sensing skin 90 includes anano-Pt/SnO₂ sensing material and/or a nano-Pd/Au/Ga₂O₃ sensingmaterial. In this embodiment, adsorbed oxygen and surface oxygenvacancies act as electron or hole trap states. The variations in oxygenvacancies result in a strong optical absorption, thereby varying therefractive index of the coated sensing material, and altering the lightcoupling between the fundamental mode and cladding mode, and thecoupling between the cladding mode and radiation mode in thelong-aperiod/period grating cladding area. This enables an observablechange in both transmission and reflection, and eventually leads to theidentification of the CO gas adsorbed. Simultaneous mapping of CO gasconcentration and localized temperature value is obtained with the samesensing module using the multi-functional and differential interrogationconfiguration of the present invention.

In a particular embodiment for incorporation into sensing system 60 at atemperature of less than about 400° C. (about 750° F.), sensing skin 90includes a base material of SnO₂. The SnO₂ base material is doped withsuitable material nanoparticles of Pd, Pt, Au, Ag and/or Ni. Thenanoparticles have a diameter of about 5 nm to about 10 nm. In thisembodiment, sensing skin 90 is prepared using a Sol-gel process or asputtering process. It is apparent to those skilled in the art andguided by the teachings herein provided that any suitable process can beused to prepare sensing skin 90. After sensing skin 90 is prepared,sensing skin 90 is annealed in an Ar⁺ environment for about 2 hours at600° C.

In an alternative embodiment for incorporation into sensing system 60 ata temperature of at least about 400° C. (about 750° F.), sensing skin 90includes a base material of Ga₂O₃. The Ga₂O₃ base material is doped withsuitable material nanoparticles of Pd, Pt, Au, Ag and/or Ni. Thenanoparticles have a diameter of about 5 nm to about 10 nm. In thisembodiment, sensing skin 90 is prepared using any suitable process knownto those skilled in the art and guided by the teachings herein provided,such as a Sol-gel process or a sputtering process. After sensing skin 90is prepared, sensing skin 90 is annealed in an Ar⁺ environment for about6 hours at 1000° C. The sensing material fabricated using theseprocesses provides adequate response and is capable of survivingprolonged operation at an elevated temperature in a highly corrosiveenvironment such as that of a boiler furnace and exhaust area.

Referring to FIGS. 5-7, in one embodiment, multi-functional sensingmodule 52, 53, 54, 55 and/or 56 is configured as a transmitive sensingmodule. In this embodiment, multi-functional sensing module 52, 53, 54,55 and/or 56 includes a first short-period fiber grating 80 positionedabout fiber core 64 and a second short-period fiber grating 82positioned about fiber core 64 and at a distance along long axis 63 withrespect to first short-period fiber grating 80. In a particularembodiment, first short-period fiber grating 80 and/or secondshort-period grating 82 includes a Bragg grating. As shown in FIG. 5, atleast one long-aperiod fiber grating (LAG) 84 and/or at least onelong-period fiber grating (LPG) 86 is positioned between firstshort-period fiber grating 80 and second short-period fiber grating 82.LAG 84 is suitable for environments wherein the temperature is at leastabout 500° C. and LPG 86 is suitable for environments wherein thetemperature is less than about 500° C. Fiber cladding 66 is positionedabout fiber gratings 80, 82, 84 and/or 86 and sensing skin 90 ispositioned about fiber cladding 66.

Referring further to FIGS. 6 and 7, in one embodiment, sensing system 60includes array 50 of multi-functional sensing modules for detecting thepresence of a chemical gas, such as carbon monoxide (CO), and measuringa temperature within boiler 12, wherein a temperature within boiler 12is greater than about 250° C. and a pressure within boiler 12 is greaterthan about 1000 psi. Array includes multi-functional sensing modules 52,53, 54, 55 and 56 having two short-period gratings 80, 82 integratedwith long-aperiod refractive index modulated grating 84 or long-periodrefractive index modulated grating 86. When broadband light is propagatethrough sensing modules 52, 53, 54, 55 and/or 56, two reflected peaksdue to Bragg resonance are detected, as shown in FIG. 6. The wavelengthshift of the two short-period fiber gratings is used to determine thelocal temperature. Further, the ratio of the Bragg peaks in thereflected power is used to detect the light loss in long-aperiod grating84, as shown in FIG. 7, to measure the CO gas concentration, regardlessof the high temperature and pressure. The temperature and the gasconcentration can be detected at each spatial location with acorresponding multi-functional sensing module 52, 53, 54, 55 and/or 56.

Referring to FIGS. 8-10, in one embodiment, multi-functional sensingmodule 52, 53, 54, 55 and/or 56 is configured as a reflectivemulti-functional sensing module. In this embodiment, multi-functionalsensing module 52, 53, 54, 55 and/or 56 includes a reference reflector92 positioned at an input end 94 of long-aperiod fiber grating (LAG) 84or long-period fiber grating (LPG) 86 and a FBG reflector 96 positionedat an opposing output 98 of LAG 84 or LPG 86 or a corresponding inputend of second short-period fiber grating 82. When broadband light ispropagate through sensing modules 52, 53, 54, 55 and/or 56, tworeflected peaks due to Bragg resonance are detected, as shown in FIG. 9.The wavelength shift of the two short-period fiber gratings is used todetermine the local pressure. The ratio of the Bragg peaks in thereflected power is used to detect the light loss in long-period grating86, as shown in FIG. 10, to measure the CO gas concentration, regardlessof the high temperature and pressure. Referring to FIGS. 9 and 10, apower loss ratio between first short-period fiber grating 80 and secondshort-period fiber grating 82 determines the presence of a particulargas, such as CO, and the concentration of the gas at the location withinboiler 12 where sensing module 52, 53, 54, 55 and/or 56 is located. Thepressure and the gas concentration can be detected at each spatiallocation with a corresponding multi-functional sensing module 52, 53,54, 55 and/or 56.

In one embodiment, sensing skin 90 includes a gas active nanoparticlematerial. In this embodiment, sensing skin 90 has a thickness thatallows a few cladding modes propagation when a refractive index ofsensing skin 90 is less than a refractive index of fiber core 64.Alternatively, sensing skin 90 has a thickness that allows a fewradiation modes propagation when a refractive index of sensing skin 90is greater than a refractive index of fiber core 64. Further, sensingskin 90 has a thermal expansion coefficient different from a thermalexpansion coefficient of fiber cladding 66 such that a material inducedinterfacial strain is controlled. In a particular embodiment, theinterfacial strain between sensing skin 90 and fiber cladding 66 isthermally compensated for by an athermal package and field calibrationbefore system operation. In an alternative embodiment, optical fibercable 62 is hermetical sealed with a hydrophobic membrane to protect thesensing modules and allow only gas penetration.

The present invention provides a method for monitoring operatingconditions and/or parameters of power generating system 10 and coalboiler 12. In one embodiment, the presence of at least one gas emittedfrom coal boiler 12 is detected and/or monitored. A broadband light ispropagated through optical fiber cable 62. Multi-functional sensingmodule 52, 53, 54, 55 and/or 56 reflects one wavelength of the broadbandlight and allows the remaining light to be transmitted through opticalfiber cable 62. Referring to FIG. 7, a wavelength peak due to Braggresonance is detected by first short-period fiber grating 80 and awavelength peak due to Bragg resonance is detected by secondshort-period fiber grating 82. This shift in wavelength corresponds to atemperature within boiler 12 where sensing module 52, 53, 54, 55 and/or56 is located. In one embodiment, the light loss is detected to measurethe power loss ratio from first short-period fiber grating 80 and secondshort-period fiber grating 82. Referring to FIG. 9, a power loss ratiobetween first short-period fiber grating 80 and second short-periodfiber grating 82 determines the presence of a particular gas, such asCO, and the concentration of the gas at the location within boiler 12where sensing module 52, 53, 54, 55 and/or 56 is located. Thetemperature and the gas concentration can be detected by onemulti-functional sensing module 52, 53, 54, 55 and/or 56.

The present invention provides a sensing system including an array offiber optic multi-functional sensing modules that are capable ofdetecting the presence of a chemical gas, a temperature and/or apressure at multiple spatial locations in a boiler environment, forexample. The fiber optic multi-functional sensing modules include afiber grating coated with a sensing skin including a chemical gas activenanomaterial. The nanomaterial has a nanoporous morphology having anaverage pore size less than about 2 microns, and the gas sensingperformance is optimized in both response amplitude and response time.Further, the fiber sensing skin is selectively highly sensitive tochemical gases by doping the base material with a noble metal catalystmaterial. When a broadband light propagates through the sensing modules,two reflected peaks due to Bragg resonance are detected, and the ratioof the Bragg peaks in the reflected power loss is used to detect thelight loss in the long-aperiod grating, regardless of the hightemperature and pressure. The absorption and adsorption processes of thetarget gas modulate the coating film optical absorption properties andthereby cause a change in the index of refraction. This index ofrefraction change modulates the couplings among fundamental code mode,cladding modes and radiation modes. The associated propagation lightloss in the sensing module will vary depending on the refractive indexvariation of the surrounding gas sensing material.

In one embodiment, the sensing skin includes an integration ofnano-Pt/SnO₂ sensing material, for environmental temperatures less thanabout 400° C., and nano-Pd/Au/Ga2O₃ sensing material for environmentaltemperatures at least about 400° C., and long-aperiod/period fibergrating. The sensing skin includes a circumferentially coated thin filmthat functions as a CO gas sensor. Adsorbed oxygen and surface oxygenvacancies act as electron or hole trap states. The variations in oxygenvacancies result in a strong optical absorption, which varies therefractive index of the coated sensing material, and alters the lightcoupling between the fundamental mode and cladding modes, and thecoupling between the cladding modes and radiation modes in thelong-aperiod/period grating-cladding area. The two short-period Bragggratings are embedded in the same environment as the long-aperiod/periodgrating. The ratio of the Bragg peaks is determined by the light lossproperties of the long-aperiod/period grating, thereby providing a novelchemical gas-sensing module. Moreover, the wavelength shift of the twoshort-period fiber gratings is used to determine the local temperature.This simultaneous detection of localized temperature and gas emissionhas improved sensor performance and reduced low false positive rate,thereby providing an accurate measurement of the CO gas concentration,regardless of temperature variations and/or other spurious events.

The multi-functional sensing module allows distributed sensingcapability for detecting multiple gases and multiple point temperatureon the same fiber cable, which is suitable for real-time detection andmonitoring in a boiler environment. The simultaneous sensing oftemperature and CO gas emission serves to cost-effectively improveboiler efficiency and to reduce CO emissions. Further, the sensingsystem of the present invention is a passive operating system with noelectric components or power requirements, and is intrinsically safe inhazardous areas that immunize electromagnetic interference and radiofrequency interference.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A system for monitoring operating conditions of a power generatingsystem, said system comprising: an optical fiber sensing cable extendingthrough at least a portion of said power generating system, said opticalfiber sensing cable having a core; an array of multi-functional sensingmodules positioned along said optical fiber sensing cable, eachmulti-functional sensing module of said plurality of multi-functionalsensing modules comprising a plurality of fiber gratings configured formonitoring at least one operating condition of said power generatingsystem, wherein each multi-functional sensing module comprises at leastone fiber grating coated with a sensing skin comprising a chemical gasactive nanomaterial; a broadband light source configured for emitting alight through said core; and an optical coupler in communication withsaid light source, said optical coupler configured for transmitting aportion of the light through said core and reflecting a portion of thelight from the plurality of fiber gratings to a photodetector.
 2. Asystem in accordance with claim 1 further comprising a computer incommunication with said photodetector, said photodetector receiving alight signal from said array, and communicating a correspondingelectrical signal to a computer.
 3. A system in accordance with claim 1wherein said nanomaterial comprises a plurality of nanoparticles havingan average diameter of about 5 nanometers to about 10 nanometers.
 4. Asystem in accordance with claim 1 wherein at least one multi-functionalsensing module of said array is configured to detect a presence of atleast one of CO, CO₂, NO_(x), O₂, H₂ and H₂S.
 5. A system for monitoringoperating conditions of a power generating system, said systemcomprising: an optical fiber sensing cable extending through at least aportion of said power generating system, said optical fiber sensingcable having a core; an array of multi-functional sensing modulespositioned along said optical fiber sensing cable, each multi-functionalsensing module of said plurality of multi-functional sensing modulescomprising a plurality of fiber gratings configured for monitoring atleast one operating condition of said power generating system, whereineach multi-functional sensing module comprises two short-period fibergratings and one of a long-aperiod fiber grating and a long-period fibergrating positioned between said two short-period fiber gratings; abroadband light source configured for emitting a light through saidcore; and an optical coupler in communication with said light source,said optical coupler configured for transmitting a portion of the lightthrough said core and reflecting a portion of the light from theplurality of fiber gratings to a photodetector.
 6. A system formonitoring operating conditions of a power generating system, saidsystem comprising: an optical fiber sensing cable extending through atleast a portion of said power generating system, said optical fibersensing cable having a core; an array of multi-functional sensingmodules positioned along said optical fiber sensing cable, eachmulti-functional sensing module of said plurality of multi-functionalsensing modules comprising a plurality of fiber gratings configured formonitoring at least one operating condition of said power generatingsystem, wherein each multi-functional sensing module comprises a sensingskin having a sensing material comprising at least one of a nano-Pt/SnO₂sensing material and a nano-Pd/Au/Ga₂O₃ sensing material; a broadbandlight source configured for emitting a light through said core; and anoptical coupler in communication with said light source, said opticalcoupler configured for transmitting a portion of the light through saidcore and reflecting a portion of the light from the plurality of fibergratings to a photodetector.
 7. A system for monitoring operatingconditions of a power generating system, said system comprising: anoptical fiber sensing cable extending through at least a portion of saidpower generating system, said optical fiber sensing cable having a core;an array of multi-functional sensing modules positioned along saidoptical fiber sensing cable, each multi-functional sensing module ofsaid plurality of multi-functional sensing modules comprising aplurality of fiber gratings configured for monitoring at least oneoperating condition of said power generating system, wherein eachmulti-functional sensing module comprises a skin having a sensingmaterial comprises at least one of SnO₂, WO_(X), Fe₂O₃ and Ga₂O₃ dopedwith at least one of Pd, Pt, Au, Ag, Ni and CuO, a broadband lightsource configured for emitting a light through said core; and an opticalcoupler in communication with said light source, said optical couplerconfigured for transmitting a portion of the light through said core andreflecting a portion of the light from the plurality of fiber gratingsto a photodetector.